This invention relates to chain saws and, more particularly, to saw chains therefor.
Conventional saw chains usually include a plurality of longitudinally spaced cutting links having a cutting tooth and a jointer or depth gauge positioned forwardly of the cutting tooth. The cutter links are connected together by center links and side links to form a continuous, articulated chain. The depth gauges are positioned to normally engage the bottom of the saw kerf so as to control the depth of cut made by the cutting teeth and to prevent undue digging of the cutting teeth into the material being cut. The saw chain is normally guided in a groove or track on the peripheral edge of a cutter bar. During travel about the outer end or nose of the cutter bar, the chain moves through an arcuate path having a relatively small radius.
When cutting is attempted with the nose portion of the cutter bar of such conventionally arranged saw chains the cutting teeth, during the initial portion of the travel around the cutter bar nose, have a tendency to attempt a cut deeper than they are capable of making. Because of the relative sharp turn the cutting links must make during this portion of traveling, the effective vertical distance between the leading depth gauge and the cutting edge of the trailing cutting tooth increases, permitting the attempted deeper penetration by the cutting tooth which can result in a kickback or upward movement of the chain saw toward the operator.
In addition, when the chain saw is used to cut timber having a relatively small diameter, such as brush or tree branches, the voids or spaces between the trailing portion of one cutting link and the leading portion of the depth gauge of the succeeding cutting link represents an area which can become locked or snagged with the branches being cut, causing a jerky operation of the chain saw and possibly even stalling of the chain saw motor or breaking of the chain.
It has been proposed to provide a saw chain with links having a guard portion which is shaped to either fill or partially fill the spaces between the cutter links so as to prevent branches from dropping into the spaces or to cam the branches out of the spaces. Examples of prior art saw chain arrangements including such a feature are disclosed in the following patents:
Robinson U.S. Pat. No. 3,329,183, issued July 4, 1967 PA1 Carlton U.S. Pat. No. 3,180,378, issued Apr. 27, 1965 PA1 Stihl U.S. Pat. No. 2,963,055, issued Dec. 6, 1960 PA1 Donley U.S. Pat. No. 2,826,226, issued Mar. 11, 1958 PA1 Carlton Canadian Pat. No. 652, 520, issued Nov. 20, 1962 PA1 Stihl Austrian Pat. No. 1,098,186, issued Jan. 26, 1961.